High Efficiency Agile Polarization Diversity Compact Miniaturized Multi-Frequency Band Antenna System With Integrated Distributed Transceivers

ABSTRACT

A compact, agile polarization diversity, multiband antenna with integrated electronics for satellite communications antenna systems is disclosed. The antenna includes a feed assembly having integrated microwave electronics that are mechanically and electromagnetically coupled thereto in a distributed arrangement so that diverse polarization senses having a low axial ratio and electronic switching control is provided. The microwave electronics include a distributed transmitter that can include high-band and low-band transceivers. The high-band and low-band transceivers can include high-band and low-band transmitter and receiver pairs, respectively. The antenna presented enables the mechanical rotation of the orientation of the high-band transceiver for skew alignment while the low-band transceiver remains stationary relative to the antenna assembly. The low-band transmitter and receiver pair can include planar interfaces electromagnetically coupled to the feed assembly between a main reflector and subreflector via OMTs. The highly compact antenna system presented offers polarization performance previously achievable by only larger devices.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/693,990 filed Aug. 28, 2012 and claims the benefit of U.S.Provisional Application No. 61/693,705 filed Aug. 27, 2012, bothentitled “Miniaturized Multi-Band Multi-Frequency Antenna with AgilePolarization Diversity.” This application is related to U.S. applicationSer. No. 13/473,690, filed on May 17, 2012, entitled “OrthomodeTransducer Device,” which claims the benefit of U.S. ProvisionalApplication No. 61/596,818, filed on Feb. 9, 2012.

The entire teachings of the above applications are incorporated hereinby reference.

BACKGROUND OF THE INVENTION

One of the most common applications of microwave technology today isradio link communications systems. Microwave (or radiofrequency (RF))communications systems can be used to provide communications links tocarry voice, data, or other signals over distances ranging from only afew meters to deep space. At a top level, microwave communicationssystems can be grouped into one of two types; guided systems or radiolinks. For guided systems, signals are transmitted over a low loss cableor waveguide. For radio links, radio signals are propagated throughspace.

One such radio link communications system is a satellite communicationssystem. A satellite communications system includes at least onecommunications satellite (COMSAT) and one or more terrestrial satellitecommunications terminals. A communications satellite is a man-madesatellite, also referred to as an artificial satellite, which is placedinto one of a variety of orbits, for example, geostationary, molniya,elliptical, and low earth, for the purposes of providingtelecommunications.

Satellite communications systems can be used to provide a number ofservices, which at the top level can be classified as providing one oftwo types of communications services: point-to-point communicationsservices, or broadcast communications services. In general, acommunications satellite acts as a microwave radio relay, receivinguplink signals from one terminal and providing a downlink to anotherterrestrial terminal at a different location. Communicationsapplications which use satellite systems include maritime, vehicular,and aviation applications, in addition to handheld devices and radio andtelevision broadcasting.

Typically, terrestrial satellite communications terminals receivedownlink signals from a satellite and, if the terminal is equipped to doso, transmit uplink signals to the satellite.

Important components in any radio link communications systems areantennas. An antenna is a component that converts a wave propagating ona transmission line to a wave propagating in free space (transmission),or a wave propagating in free space to a wave propagating on atransmission line (reception). A wide variety of antenna types andgeometries exist, including aperture antennas, reflector antennas,phased array antennas, and combinations thereof.

Antennas are particularly important in satellite communications systems,as can be seen from the Friis power transmission formula:

${P_{r} = \frac{P_{t}G_{t}G_{r}\lambda^{2}}{\left( {4\pi \; R} \right)^{2}}};$

where P_(r) is power received, P_(t) is power transmitted, G_(r) is thegain of the receive antenna, G_(t) is the gain of the transmit antenna,R is the distance between the antennas, λ is the wavelength of thesignal of interest and it is assumed that the main beams of the antennasare aligned. Further the effective gain, G, of an antenna can beexpressed in terms of an effective area,

${A_{e}\text{:}G} = {\frac{4\pi \; A_{e}}{\lambda^{2}}.}$

The effective area, A_(e), is directly related to the physical area, A,of an antenna by the antenna efficiency, η_(a), or aperture efficiency:A_(e)=η_(a)A. According to the Friis power transmission formula, thepower density received at a receive antenna is inversely proportional tothe square of the distance the signal travels from the source. Becausesatellite communications links are used to communicate over greatdistances, the gains provided by the antennas are particularlyimportant.

Aperture antennas are often flared sections of waveguide, typicallyreferred to as a horn antenna, or are simply open-ended waveguide. Suchantennas are commonly used at microwave frequencies and have moderateantenna gains. Antennas of this type are often used for aircraft andspacecraft applications because they can be conveniently flush mountedon the skin of the vehicle and filled with a dielectric material toprovide protection to the aperture from the hazardous conditions of theenvironment while maintaining the aerodynamic properties of the vehicle.

Reflector antennas are typically used for applications requiring highantenna gain, such as satellite communications system. The high gainsprovided by reflector antennas are useful for increasing the range of amicrowave system. Usually, the high gains provided by such antennas areachieved by focusing the radiation from a small antenna feed onto anelectrically larger reflector. An antenna feed is a component of anantenna that couples electromagnetic energy (e.g., microwaves or RFwaves) to or from a focusing component of the antenna structure, such asa reflector. In other words, for transmission, an antenna feed guides RFenergy from a transmission line to a reflective and directive structurethat forms the RF energy from the antenna feed into a beam or otherdesired radiation pattern for propagation in free space. For reception,the process is reversed. The reflecting structure focuses RF energy tothe antenna feed, which collects the incoming RF energy. The RF energyis then propagated along a transmission line to the receiver. Often, theantenna feed is a dipole, feed horn or, simply, even an open-endedwaveguide.

Reflector antennas typically include a feed and additional reflectiveand directive structures, such as a parabolic dish or parasiticelements, whose function is to form the radio waves from the feed into abeam or other desired radiation pattern. Often, reflector antennas areprotected from the environment by enclosing them within a radome. Aradome is, ideally, an electrically invisible structure that providesprotection from the environment for the antenna. If the radome iselectrically invisible to the antenna (or approximately transparent), itwill not degrade antenna performance significantly. Radomes aretypically made from low dielectric hydrophobic materials.

Reflector antennas, of which a parabolic dish antenna is a specifictype, are relatively easy to fabricate and are typically quite rugged.However, such antennas can be quite large and unwieldy to move. Becauseof this, robust mechanical systems are typically needed to steerreflector antennas. The directive beam of a reflector antenna istypically directed along the bore sight axis of the parabolic dish andsteered solely by mechanical means used to rotate or otherwise adjustthe angular direction of the parabolic dish.

Phased array antennas include multiple stationary antenna elements,typically identical, which are fed coherently and use variable phase ortime delay control, or a combination thereof, at each element to scan adirective beam to a given angle in space. Variable amplitude control canalso be used to provide beam pattern shaping. Examples of typical phasearray antenna elements, also called radiators, include dipoles,microstrip, or patch elements. The primary advantage of the phased arrayantenna over more traditional antenna types, such as aperture andreflector antennas, is that the directive beam can be repositionedelectronically, i.e., scanned electronically. Electronic beam steeringcan be useful for quickly and accurately redirecting a beam.

Hybrid antennas, such as reflector antennas with a phased array feed,combine useful characteristics of both antenna types, such as the highgain and/or robust design of a reflector antenna, and the agileelectronic steering capabilities of the phased array antenna. Althoughnot typically used due to the design costs outweighing the increasedperformance, a hybrid reflector antenna with a phased array feed can beelectronically scanned over a limited angular region.

Polarization is an important characteristic of all electromagneticwaves. Polarization describes the motion through which an electric fieldvector of an electromagnetic wave points as the electromagnetic wavetravels through a point in space. The electric field vector tip cantrace a line, circle, or ellipse as the electromagnetic wave passesthrough the imaginary point in space. In general, these traces arereferred to as linear, circular, or elliptical polarization,respectively.

Polarization is important in many applications, and particularly forantennas. The polarization of the antenna is defined by theelectromagnetic wave it radiates when the antenna is transmitting. Thepolarization characteristic of the antenna is important because, formaximum power transfer between radio links, the transmitting andreceiving antennas must be of identical matching polarization states atthe same time. If the transmitting and receiving antennas areorthogonally polarized, for example, the transmitting antenna ishorizontally polarized while the receiving antenna is verticallypolarized, then no power would be received. Conversely, if both thetransmitting and receiving antennas are horizontally or verticallypolarized, then maximum power is received. Because antennas facilitatethe transition of electromagnetic energy propagating between free spaceand a transmission link, polarization is also an importantcharacteristic of all antennas.

Many microwave systems, such as satellite communications systems, relyon waveguide transmission lines for low loss guided propagation ofmicrowave power. Such waveguide systems or networks are typically usedas part of an antenna feed. A waveguide, which is typically arectangular or circular tube with conducting walls, is capable ofhandling high power microwave signals, but is bulky and expensive.Because waveguides include only a single conductor, they supporttransverse electric (TE) and transverse magnetic (TM) waves, which arecharacterized by the presence of longitudinal magnetic or electric fieldcomponents, respectively. Waveguides are one of the earliest types oftransmission lines developed to transport microwave signals and arestill used today. Because waveguide technology is mature, there are alarge selection of waveguide components, such as splitters/combiners,couplers, detectors, isolators, attenuators, phase shifters, and slottedlines commercially available for various standard waveguide bands from 1gigahertz (GHz) to over 220 GHz. Due to the recent trend towardminiaturization and integration, many microwave circuits are currentlybeing fabricated using planar transmission lines, such as microstrip andstripline, instead of waveguide. However, the performance required formany high power applications, such as satellite communications systems,and, in particular, antenna feed assemblies for such systems,necessitates the use of waveguides.

For the sake of design simplicity, most waveguide-based transmissionline systems support only a single propagating mode, known as the“fundamental” mode. The single fundamental propagating mode is typicallythe first mode that propagates through the waveguide having a frequencyabove the cut-off frequency of the waveguide. Waveguides can becharacterized as high pass filters as they enable signals above thecut-off frequency to propagate and attenuate all signals below thecut-off frequency. Due to the inverse relationship between wavelengthand frequency, higher frequency waveguide components, such as Ku-bandsystems, have smaller dimensions than lower frequency components, suchas C-band systems. In high-power systems, voltage breakdown or arcingcan occur when the dielectric (typically air for waveguides) separatingconducting walls breaks down. Such arcing is more likely to occur inhigh-powered, high frequency systems because of the relatively smalldimensions and, thus, lower breakdown voltage, between conductors.

Typically, the fundamental mode or another low-order mode, couples wellwith a free-space radiating beam. In other words, the low-order mode iswell matched, and, thus, transfers energy efficiently to free space. Insuch instances, the propagating mode represents the beam pattern at thefeed horn, which illuminates the focusing reflector of a reflectorantenna. Generally, the goal is to have a pure single mode at the feedto minimize beam distortion.

SUMMARY OF THE INVENTION

A miniaturized, compact, multi-frequency band antenna having agilepolarization diversity and a high antenna efficiency is presentedherein. Example embodiments of the antenna system include an antennafeed with integrated electronics in a distributed configuration. Exampleembodiments of the antenna system can be used for satellitecommunications, such as the antenna system of a very small apertureterminal (VSAT). The antenna system includes an antenna feed havinghighly integrated microwave electronics that are mechanically andelectromagnetically coupled thereto in a distributed arrangement so thatdiverse polarization senses having a low axial ratio (or highpolarization isolation characteristics) are achieved. The microwaveelectronics can include multiple transceivers. The multiple transceiverscan include transmitter and receiver modules, which can be coupled tothe antenna feed in a distributed arrangement. For example, thedistributed arrangement can include coupling to receive and transmitports, or sets of ports, separated by a distance of wavelengths. Theantenna feed can be arranged to mechanically rotate the orientation of afirst transceiver relative to the second transceiver. Electronicswitching control of the polarization sense is provided by exampleembodiments. The antenna system presented is highly compact and offersimproved polarization performance previously achievable by only largerdevices.

Dual-reflector antenna designs, antennas having a subreflector and mainreflector configuration, are used widely for multiple frequency bandantenna applications. One of the advantages of such dual-reflectorantennas is provided when a multi-band feed assembly is placed betweenthe main reflector and its focal point to reduce the size of the radomeneeded to protect the antenna.

Multiple frequency band feed systems traditional include a common path,such as a center waveguide, that is able to support the propagation ofall the multi-band signal components. In order to multiplex using suchtraditional feeds, individual coupling ports, also referred to asirises, are placed at different locations along the center waveguide.Signals within a specific frequency band couple through these ports andare propagated along transmission lines leading to and from transceivers(or a transmitter-receiver pair) traditionally located behind the maindish. In order to reduce attenuation and energy loss along thepropagation path, waveguide networks have been traditionally used. Thedimensions of the waveguide networks are determined by the frequency ofthe signals of interest. The lower the frequency, the larger thewaveguide cross-section. In order to minimize the waveguide feed linelength and reduce the weight and size of the feed assembly, thewaveguide feed networks are usually shaped with different bends andtwists. Although historically feed networks containing such bends andtwist were the most preferred solution, the bends and twists increasedmanufacturing and system complexity, and degraded system performancefrom the ideal.

Presented herein, is a multi-frequency band antenna having aminiaturized distributed transceiver module that is integrated with theantenna feed and can include more than one transceiver to supportcommunications links over the multiple frequency bands. In oneembodiment, the distributed transceiver module, which can include a lownoise block (LNB) receiver module and a solid state power amplifier(SSPA) transmitter module, which are both designed into a short,cylindrical form factor having an opening in the center. Thecylindrical-shaped (disk-shaped or ring-shaped) receiver and transmittermodules can be integrated with the feed assembly in front of a maindish. The center opening of such modules allows a pass-througharrangement of a common waveguide feed and allows the common waveguidefeed to propagate signals unimpeded through the modules.

In some example embodiments, each transmitter and receiver module hasfour waveguide coupling ports arranged orthogonally that mate to thecoupling ports on the common center waveguide directly, which minimizesattenuation and signal loss. Put another way, each transmitter andreceiver pair is coupled to the antenna feed using an orthomodetransducer (OMT). The LNB module amplifies received satellite signals toa high level such that additional signal loss by inexpensive cablesbetween the receiver and modem do not degrade the quality of thereceived signals. Furthermore, the SSPA amplifies the uplink signal to ahigh power level, suitable for satellite communications, and couplesdirectly into the waveguide ports. Thus, only a couple of SMA cablesneed be used to connect the individual LNB and SSPA modules to transmitthe signals to the back of the dish; no lengthy waveguide feed lineshaving complicated bends and twists are needed. The transmitter andreceiver module locations proximal to coupling ports along the centerwaveguide obviate a waveguide feed network. The result is ahighly-compact and lightweight feed module, which, for C/Ku-bands, has a9.2 inch diameter, compared to a 17 inch diameter for a feed assemblyfor traditional C-band-only dual reflector antennas. With such a smallerfeed assembly, a compact C/Ku antenna with a dish diameter of 42.3inches, a radome size of 48 inches, and an antenna efficiency of about60-75% is achieved. When compared to traditional C-band dual reflectorantennas which have a 17 inch feed assembly and an antenna dish diameterof 106.3 inches, the size reduction of the example embodiment issubstantial.

Example embodiments of the invention described herein may be designedfor the C-band and Ku-band applications, but, as will be understood bythose of skill in the art, other embodiments may be used forapplications at many other frequency bands and combinations of frequencybands.

In some embodiments, a C-band receiving module (C-band LNA circuit) isintegrated at the output of the C-band receiving waveguide multiplexer(or combiner) directly, which minimizes insertion loss and improvessystem gain over temperature (G/T) performance.

The example integrated C-band receiving module has a center opening toallow higher frequency signals, such as C-band transmitting signals andKu-band signals, to pass through unimpeded. Further, the C-band receivemodule is arranged between the main reflector and the feed horn.

The integrated C-band receiving module may incorporate a polarizationnetwork at the front end to enable switchable inputs for right-handcircular polarized (RHCP) or left-hand circular polarized (LHCP)signals.

The example integrated C-band receive module, located in front of themain reflector, is arranged to stay behind the low-frequency (i.e.,C-band receive frequency band) waveguide combiner and subreflector. Thisarrangement provides for minimum antenna efficiency degradation.

In some embodiments, a C-band transmitting circuit including poweramplifier circuit, is integrated directly at the input of the C-bandtransmitting waveguide combiner. This arrangement reduces losses betweenthe power amplifier circuit and antenna feed, allows for lower poweramplification, obviates a bulky waveguide feed line, and reduces systemcomplexity and cost.

The example integrated C-band transmitting module has a disk-shape witha center opening to allow higher frequency components, such as Ku-bandsignals to pass through.

The example integrated C-band transmitting module incorporates apolarization network to enable switchable outputs of RHCP or LHCPsignals.

Example polarization networks in both the C-band transmitting andreceiving circuits are independently selectable, enabling great systemflexibility.

The polarization networks in both the C-band transmitting and receivingcircuits also use matched termination to terminate the idling port whenthe polarization sense in not in use. This design improves thepolarization performance of the network.

The integrated C-band transmitting circuit utilizes the metal structureof the entire feed to dissipate heat, which reduces the required size ofadditional heat dissipation hardware, such as cooling fans, heat-sinks,heat-pipes and/or any combination thereof.

C-band multiplexer/combiner, feed horn, and C-band integratedelectronics are fixed into position without rotation about the centeraxis of the reflector antenna. By incorporating a circular waveguiderotary union (or joint), in one embodiment, only the Ku-band combinerrotates to align the linear signal polarization to the satellite (alsoknown as skew alignment).

The relatively large C-band waveguide combiners and transceiver modules,located in front of the main reflector, stay inside the “shadow” of thesub-reflector, minimizing additional blockage of the antenna aperture.This configuration enables a highly integrated feed network and antennahorn. It further enables the overall feed system to be much more compactthan other dual-band VSAT systems, thus minimizing the impact on antennaefficiency, and reduces the weight, cost, and complexity of the entireantenna while enhancing the system performance at the same time.

In an example embodiment of a stabilized antenna systems using a compactfeed as disclosed herein, the larger and heavier C-band portion of themultiband feed network remains fixed near the vertex of the reflectorand the weight center (i.e., center of inertia) of the system providingeasier balancing of and movement in the azimuth and elevation rotationof the stabilized antenna, enabling reduction in power and weight motorsemployed to steer the antenna.

In one embodiment, a centralized switch and control module connects tothe integrated C-band receiving and transmitting modules and the Ku-bandtransceiver to provide control signals, DC power, signal switching, andsignal-level control. This arrangement delivers a unified and seamlessinterface to an external modem, thereby reducing the system complexityfor installation and operation. The Ku-band transceiver may be mountedat the end of the entire feed system in an example embodiment. TheKu-band transceiver provides the Ku VSAT operation capability for anexample antenna.

The example centralized switch and control module connects to theintegrated C-band receiving and transmitting modules, and Ku-bandtransceiver. The centralized switch and control provides DC power,reference signals, control signals, intermediate frequency (IF) signals,and/or radio frequency (RF) signal to the C-band receiving andtransmitting modules and the Ku-band transceiver.

In some embodiments, the centralized switch and control module providesswitching between C-band and Ku-band VSAT operation. It delivers asimple and unified interface to the external modem and reduces systemcomplexity for installation. In some embodiments, the centralized switchand control module enables simultaneous operations, i.e., simultaneousreception and transmission, at either the C-band or Ku-band.Furthermore, it will be recognized by those of skill in the art that,some embodiments, for example, embodiments including two modems ordual-band modem, enable simultaneous reception and transmission at bothC-band and Ku-band when paired with a satellite capable of simultaneousC-band and Ku-band operation.

The centralized switch and control module may provide intermediatefrequency (IF) signal level control to enable various IF cable lengthsfor various system installations.

The centralized switch and control module may also perform frequency upconversion for C-band transmit signal. This arrangement reduces theweight of the integrated C-band transmitting module.

In an example embodiment including a centralized switch and controlmodule, switching between C-band and Ku-band VSAT operation may beprovided. A centralized switch and control module may provide a simpleand unified interface to the modem and reduces system complexity forinstallation. The centralized switch and control module also may providean intermediate frequency (IF) signal level control to enable variousembodiments.

In some embodiments, a compact, dual-polarized, multiband, waveguidecombiner (also referred to herein as a multiplexer) with integratedelectronics for use in satellite communications antenna systems ispresented. The waveguide combiner (or multiplexer) providesdual-polarized signal filtering of three (or fewer or more) separatefrequency bands. For the two lowest frequency bands in some exampleembodiments, highly integrated microwave electronics are coupled to thewaveguide combiner device to generate the desired polarization sensewith improved polarization performance and electronic switching controlof the polarization sense. This multiband combiner design is highlycompact and offers improved polarization performance previouslyachievable only by larger waveguide devices.

In an example embodiment, a dual-polarized waveguide combiner providessignal filtering of three (or fewer or more) separate frequency bands:(i) C-band Receive 3.600 to 4.200 GHz; (ii) C-band Transmit 5.850 to6.425 GHz; and, (iii) Ku-band Receive (11.700 to 12.700 GHz) and Ku-bandTransmit (14.000 to 14.500 GHz) band 11.700 to 14.500 GHz.

In some example embodiments, the waveguide combiner includes a commonport that propagates all frequency bands with two orthogonalpolarizations. A first set of four waveguide paths with coupling irisesare attached to the common dual-polarized waveguide to couple the lowestfrequency band signals. A second set of four waveguide paths withcoupling irises are attached to a reduced-size of the dual-polarizedwaveguide to couple the intermediate frequency bands signals. A furtherreduced size, dual-polarized back (or rear) port propagates the highestfrequency band signals.

The first set of phase-matched low loss waveguide paths may integrate ina single plane in order to facilitate the connections to a microstripline printed circuit board (PCB) network. In such an embodiment, signalsplitting and phase delays required to receive the desired state ofpolarization are included the PCB networks. In the case of the receivewaveguides, the transmit rejection filter is integrated into waveguide“sweeping arms” to minimize the combiner size. Each of the four receivewaveguide paths of the corresponding waveguide sweeping arms includeidentical waveguide path and coupling structures to the receivemicrostrip network PCB interfaces. The four receive waveguide sweepingarms interface in a plane in one embodiment. Optionally, each of thefour receive waveguide paths include 90 degree waveguide bends. Thesymmetrical and opposing waveguides defining the waveguide paths (e.g.,the waveguide sweeping arms) may bend in opposing directions.Alternatively, the symmetrical and opposing waveguides may bend insimilar directions. A PCB with a microstrip or stripline networkinterfaces to the waveguide interface plane. The receive band microstripcombiner may provide amplitude and phase relationships to receivecircularly polarized signals.

The second set of phase-matched, low loss, waveguide paths of an exampleembodiment integrates in a single plane in order to facilitate theconnections to a microstrip or stripline PCB network. The signalsplitting and phase delays required to produce the desired state ofpolarization may be included in the PCB networks. Each of the fourtransmit waveguide paths include identical waveguide path and couplingstructures to the transmit microstrip network PCB interfaces. The fourtransmit waveguide arms interface in a plane. Optionally, each of thefour transmit waveguide paths include 90° waveguide bends.Alternatively, the symmetrical and opposing waveguides bend in opposingdirections. The symmetrical and opposing waveguides bend in similardirections. A PCB with a microstrip or stripline network interfaces tothe waveguide plane. The transmit band microstrip combiner may providethe necessary amplitude and phase relationships to create circularlypolarized signals. A symmetrical low loss waveguide provides adual-polarized signal path through the waveguide combiner body for thehighest frequency band. In one configuration, a low loss, circular,dielectric rod is used to propagate the highest frequency band signalsthrough the combiner. In this case, dual polarized Ku-band signalspropagate through the dielectric rod within the C-band, dual polarized,metallic waveguide.

Other frequency band combinations are feasible; for example, an exampleembodiment can be configured to be used for a C-band and Ka-bandmultiband system, X-band and Ka band multiband system, Ku-band andKa-band multiband system, or the like.

Electronic polarization switching may be included in the PCB networks.The C-band transmit and/or receive PCB networks include a means toswitch electronically between the circular polarization, RHCP, and LHCP.Other embodiments are configured to support linear polarization.

The C-band transmit and receive PCB networks provide a matchedtermination to reflected signals of the opposite polarization sense,thereby improving the overall antenna polarization performance.

An example embodiment is applicable as a dual-band, dual-polarized,waveguide combiner providing signal filtering for separate frequencybands, for example, C-band Receive 3.625 to 4.200 GHz and C-bandTransmit 5.850 to 6.425 GHz.

In embodiments of the present invention, a miniaturized polarizationagile and diverse multi-frequency VSAT antenna is achieved and therebyreduces the physical size of the antenna. Generally, suchminiaturization is enabled through a reduction in the size of theantenna feed and waveguide assembly in conjunction with the distributionand integration of the multi-frequency transceiver modules. Moreparticularly, the low frequency band receivers and transmitters areminiaturized and integrated with the antenna feed. The low frequencytransceiver can include a receiver module and a transmitter module. Thereceiver module and transmitter module both have a form factor of ashort cylindrical shape with an opening in the center. In other words,they may be disk-shaped, ring-shaped, or washer-shaped. Thecylindrically shaped modules can be integrated into a feed assembly infront of the main dish, and the center opening of the modules allows thefeed assembly's common waveguide to propagate signals through to higherfrequency transceivers. In an example embodiment, each receiver andtransmitter module has four coupling ports that couple to the centerwaveguide feed and meet to planar coupling ports on the modules. Theshort waveguide paths that couple from coupling irises located on thecenter waveguide path via waveguides to the planar interface ports alongthe transceiver modules minimizes signal attenuation along thisembodiment. An embodiment avoids the use of a lengthy complicatedwaveguide feed lines containing typical bends and twists. Due to thefact that a complicated waveguide feed line is obviated in order tobring the signal to the rear of the rear-fed reflector, a compact andlightweight feed assembly results. In an example embodiment, the C-bandand Ku-band feed module is about 9.2 inches in diameter and feeds aC-band and Ku-band antenna parabolic dish with diameter of 42.3 inches.The antenna efficiency of this example embodiment is about 75%±8% forKu-band and 65%±11% for C-band, or more or less, depending on systemperformance budgets.

In one embodiment, an antenna feed assembly includes a feed horn, set ofphase matched RF paths, receiver module mounted to the feed horn andcoupled to the RF paths and a subreflector. The feed horn is configuredto propagate multiple radio frequency (RF) bands with primary radiationpatterns having substantially the same beam width for at least two RFbands of the multiple RF bands. The two RF bands may be RF transmittingbands. The set of phase matched RF paths are operative over an RF bandof the multiple RF bands, electromagnetically coupled to the feed hornand configured to propagate electromagnetic energy of correspondingpolarizations in an orthogonal arrangement around the feed horn. Thereceiver module may be monitored to the feed horn and mechanically andelectromagnetically coupled to the set of RF paths. The subreflector mayhave a lateral cross-section of the same dimension or larger than acorresponding lateral cross-section of the feed horn and mountedreceiver module. The receiver module may include an electric phaseshifter operative to adjust a phase length or phase angle (or setting)of electromagnetic energy received via the set of phase matched RFpaths. The electronic phase shifter of the receiver module may controlswitching between receiving electromagnetic signals having a right handcircular polarization (RHCP) sense and a left hand circular polarization(LHCP) sense independently of a transmitter function of a transmittermodule. The set of phase matched RF paths can be a first set of phasematched RF paths and the RF band can be a first RF band. The antennafeed assembly may further include a second set of phase matched RF pathsoperative over a second RF band of the multiple RF bands and may beelectromagnetically coupled to the feed horn and configured in anorthogonal arrangement around the feed horn. The antenna feed assemblymay further include a transmitter module mounted to the feed horn andmechanically and electromagnetically coupled to the second set of RFpaths. The transmitter module may include an electronic phase shifteroperative to adjust a phase length or phase angle (or setting) ofelectromagnetic energy to be transmitted via the second set of phasematched RF paths. The electronic phase shifter of the transmitter modulemay be configured to control switching between transmittingelectromagnetic signals having a RHCP sense and a LHCP senseindependently of a received function of the receiver module.

In another example embodiment, an antenna assembly including an antennafeed assembly and first and second transceivers mechanically andelectromagnetically coupled to respective receive and transmit ports ofthe antenna feed assembly. The antenna feed assembly is arranged torotate mechanically an orientation of the first transceiver relative tothe orientation of the second transceiver. The first and secondtransceivers operate over first and second RF bands, respectively. Thefirst RF band may include a range of Ku-band frequencies. The second RFband may include a range of C-band frequencies. Bands with the same orother frequencies are also contemplated to be within the scope of thisand other embodiments. The antenna assembly may also include a mainreflector arranged in a stationary orientation relative to the secondtransceiver. The antenna assembly may also include a subreflectorconfigured to reflect electromagnetic energy propagating between theantenna feed assembly and the main reflector. The subreflector createsan RF shadow region or blockage region. In some example embodiments, thesecond transceiver is at least partially located within the RF shadowregion. Alternatively, or additionally the second transceiver isarranged such that a cross-section of the second transceiver can beentirely located within the region created by the subreflector. Thefirst transceiver may be arranged to rotate to enable linearpolarization alignment with a paired antenna distal from the antennaassembly, also known as skew alignment. The antenna assembly can furtherinclude transmit and receive planar coupling interfaces. The secondtransceiver can be mounted to the antenna feed assembly such thatcoupling between the transmit and receive ports of the secondtransceiver and corresponding transmit and receive ports of the antennafeed assembly occurs at the transmit and receive planar couplinginterfaces, respectively. The antenna assembly may further include asubreflector configured to reflect electromagnetic energy propagatingbetween the antenna feed assembly and the main reflector, thesubreflector creating RF shadow region (electromagnetic blockage region)from a far-field perspective between the subreflector and the mainreflector. The transmit and receive planar coupling interfaces can belocated within the RF shadow and have lateral dimensions that do notprotrude from the RF shadow region.

An example method of the present invention includes a method oftransitioning propagating microwave energy between a transmission lineand free-space using an antenna assembly, the method includespropagating microwave energy using an antenna feed assembly, couplingthe propagating microwave energy to first and second transceiversmechanically and electromagnetically coupled to respective receive andtransmit ports of the antenna feed assembly, and rotating mechanicallyan orientation of the first transceiver relative to the secondtransceiver. The propagating microwave energy can be over first andsecond RF bands, the first and second RF bands being the operationalbands or within the operational bands of interest of the first andsecond transceivers, respectively. The propagating microwave energy ofthe first RF band can be comprised of a range of substantially Ku-bandfrequencies and the propagating microwave energy of the second RF bandcan be comprised of a range of substantially C-band frequencies. Theexample method can further include facilitating the propagatingmicrowave energy of the first RF band within the antenna feed assemblythrough the use of a dielectric rod. The example method can furtherinclude maintaining a stationary orientation of a main reflectorrelative to the second transceiver. The example method can furtherinclude reflecting electromagnetic energy propagating between theantenna feed assembly and the main reflector using a subreflector, thesubreflector creating an RF shadow region, and transmitting or receivingusing the second transceiver, the second transceiver being at leastpartially located within the RF shadow region. The transmitting orreceiving is performed by a transmitter and receiver, respectively,composing the second transceiving the second transceiver having alateral cross-section entirely located within the RF shadow region. Therotating mechanically the orientation of the first transceiver canfurther include rotating the first transceiver to enable linearpolarization alignment with a paired antenna distal from the antennaassembly. The coupling of the propagating microwave energy to the secondtransceivers can be performed at the transmit and receive ports of thesecond transceiver and corresponding respective transmit and receiveports of the antenna feed assembly at transmit and receive a planarcoupling interfaces. The example method can further include reflectingelectromagnetic energy propagating between the antenna feed assembly andthe main reflector using a subreflector, the subreflector creating an RFshadow region, and transmitting and receiving using the secondtransceivers the transmit and receive planar coupling interfaces beinglocated in the RF shadow region and having maximum lateral dimensions nogreater than corresponding lateral dimension of the RF shadow region.

An example embodiment of an antenna feed assembly can include means forpropagating microwave energy to feed an antenna assembly, means forcoupling the propagating microwave energy to first and secondtransceivers having means for mechanically and electromagneticallycoupling to respective receive and transmit ports of the antenna feedassembly, and means for mechanically rotating an orientation of thefirst transceiver relative to the second transceiver.

Yet another example embodiment includes an antenna assembly including afeed horn assembly having symmetry about an axis of propagation, a setof RF propagation paths, and a distributed receiver coupled mechanicallyand electromagnetically to the set of RF propagation paths at a set ofreceive ports. The set of RF propagation paths may beelectromagnetically coupled to the feed horn assembly and configured topropagate electromagnetic energy of an RF band parallel to the axis ofpropagation. The antenna assembly may further include a receiversubcircuit of the distributed receiver, the receiver subcircuit can bearranged to shift electronically a phase of electromagnetic energyreceived at the set of receive ports. The set of RF propagation pathsmay be further configured in an orthogonal arrangement around the axisof symmetry of the feed horn assembly. The receiver subcircuit of thedistributed receiver may enable electronic switching betweenelectromagnetic energy having a right hand circular polarization (RHCP)sense and a left hand circular polarization (LHCP) sense. The antennaassembly may further include a main reflector and a subreflector, wherethe subreflector is configured to reflect electromagnetic energypropagating between the antenna feed assembly and the main reflector,the subreflector creating an RF shadow region. The distributed receiverand set of RF propagation paths may be located within the RF shadowregion and have respective lateral cross-sections that do not exceed alateral cross-section of the RF shadow region. In other words, thedistributed receiver and set of RF paths, in one embodiment, do notprotrude from the RF shadow on the main reflector created by thesubreflector. The set of RF propagation paths can be a first set of RFpropagation paths, and the RF band can be a first RF band, the antennaassembly may further include a second set of RF propagation pathscoupled to the feed horn assembly. The second set of RF propagationpaths may be configured to propagate electromagnetic energy of a secondRF band parallel to the axis of propagation. The antenna assembly mayfurther include a distributed transmitter circuit coupled mechanicallyand electromagnetically to the second set of RF propagation paths at aset of transmit ports. A transmitter subcircuit of the distributedtransmitter may be arranged to shift electronically phase ofelectromagnetic energy transmitted at the set of transmit ports. Thesecond set of RF propagation paths may be further configured in anorthogonal arrangement around the axis of symmetry of the feed hornassembly. The transmitter subcircuit may switch electronically betweenelectromagnetic energy having a RHCP sense and a LHCP sense. Thetransmitter subcircuit may provide polarization switching independentlyof a receiver polarization state. The antenna assemble can furtherinclude a dielectric rod having an axis coincidental with the axis ofpropagation of the feed horn assembly.

Still another example embodiment includes an antenna feed assemblyincluding phase shifting electronics, mechanically andelectromagnetically coupled to ports of the antenna feed assembly, and acontroller, operatively coupled to the phase shifting electronics andconfigured to enable the phase shifting electronics to switch betweenright hand circular polarization (RHCP) and left hand circularpolarization (LHCP) senses. The phase shifting electronics areassociated with a transceiver, having a transmitter circuit or moduleand a receiver circuit or module, and further configured to switchindependently transmitter and receiver polarization senses.

A still further example embodiment includes a rear-fed reflector antennaassembly including a feed horn assembly, a coupling structure, and areflector. The feed horn assembly may include a feed horn, subreflectorwaveguide assembly, having ports coupled to the feed horn, and microwavecircuits electromagnetically coupled to the ports via a couplingstructure. The reflector may be electronically coupled to the feedassembly in a rear feed arrangement in which at least a subset of themicrowave circuits are located between the subreflector and thereflector. The microwave circuits may include transmitter and receivercircuits. In this example embodiment, the feed horn is configured topropagate RF signals at multiple RF bands with primary radiationpatterns having substantially the same beam width for two (or more) ofthe RF transmission bands. Put another way, the feed horn may beconfigured such that the antenna pattern has substantially the samebeamwidth for multiple frequency bands, e.g., beam widths within about 2dB of each other for about 35° off of bore sight.

Yet another example embodiment includes a rear-fed reflector antennaassembly including a main reflector having a greatest dimension that isbetween 10 and 20 times greater than the wavelength in a wavelengthrange of interest and a subreflector arranged to reflect electromagneticenergy propagating between the main reflector and an antenna feedassembly mechanically coupled to the main reflector and a pass througharrangement, the subreflector optionally having a greatest dimensionbased on a minimum antenna efficiency and an RF shadow on the mainreflector. The antenna feed assembly may be arranged between the mainreflector and the subreflector and have a greatest dimension confinedwithin the electromagnetic shadow. In an example embodiment, the mainreflector may have its greatest dimension of about 1 meter. The rear-fedreflector assembly may further include ring-shaped transmitter andreceiver modules mounted to the antenna feed assembly the ring-shapedmodules being mounted to the exterior of the antenna feed assembly andat least partially between the main reflector and subreflector. Thetransmitter and receiver module can have respective transmit and receiveplanar interfaces having respective greatest lateral dimensions that fitwithin the RF shadow. The wavelength range of interest may be betweenabout 2.07 cm (14.50 GHz) and 8.30 cm (3.60 GHz). This wavelength rangeof interest includes the C-band transmission frequency band. The antennafeed assembly may have a primary radiation pattern having substantiallythe same beamwidths (e.g., within about 2 dB for range of angles frombore sight to about 35° off of boresight) for each of the multiplewavelength ranges, including the wavelength range or ranges of interest.The wavelength range of interest may be between about 4.67 cm and 8.30cm. And, the multiple wavelength ranges of interest may further includea second wavelength range of interest between about 2.07-2.56 cm(14-14.5 GHz). It should be understood that other frequency bands arewithin the scope of the present invention.

In a still further example embodiment, an antenna assembly, includes amain reflector, an antenna feed assembly, arranged to be stationaryrelative to the main reflector and being in a pass-through arrangementwith the main reflector, the antenna feed assembly including asubreflector, configured to reflect electromagnetic energy propagatingbetween the main reflector and a feed horn, a waveguide assembly, havingsymmetry about an axis of propagation, the respective waveguide assemblyconfigured to support propagation of at least a first radio frequency(RF) band and second RF band, the waveguide assembly including, the feedhorn, configured to propagate the first and second RF bands withrespective primary radiation patterns having substantially the samebeamwidth, a first orthomode transducer (OMT), having a first set of RFpropagation paths operative over a receive frequency band of the firstfrequency band and arranged in quadrature around the axis of propagationof the waveguide assembly, the first OMT electromagnetically couplingthe waveguide assembly to a set of receive ports at a receiver planarinterface between the first OMT and a first transceiver of a distributedtransceiver, a second OMT, having a second set of RF propagation pathsoperative over a transmit frequency band of the first frequency band andarranged in quadrature around the axis of propagation of the waveguideassembly, the second OMT electromagnetically coupling the waveguideassembly to a set of transmit ports at a transmit planar interfacebetween the second OMT and the first transceiver of the distributedtransceiver, and a dielectric rod configured to facilitate propagationof electromagnetic energy, having a frequency or range of frequencieswithin the second RF band, through the waveguide assembly, thedielectric rod being arranged along the axis of propagation of thewaveguide assembly, a third OMT mechanically and electromagneticallycoupled to the waveguide assembly and to a second transceiver of thedistributed transceiver, the second transceiver being operative over thesecond RF band or a portion of the second RF band, and the first andsecond transceivers composing the distributed transceiver, the firsttransceiver including a receive module and a transmit module, thereceive and transmit modules being disk-shaped and mounted to thewaveguide assembly in a pass-through arrangement, the receiver andtransmitter planar interfaces being located between the subreflector andthe main reflector, and the antenna assembly further including a driveassembly configured to rotate mechanically an orientation of the secondtransceiver relative to the first transceiver.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing will be apparent from the following more particulardescription of example embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingembodiments of the present invention.

FIG. 1A depicts an example application of an example embodiment of thepresent invention.

FIG. 1A-1 is a diagram of an embodiment of the present invention antennaassembly radome depicted relative to a prior art radome.

FIG. 1B illustrates a VSAT including an antenna unit and below deckequipment.

FIG. 2 is a satellite coverage map provided by a dual-frequency VSATassembly.

FIG. 3 illustrates a significant reduction in size possible with anexample embodiment of the present invention.

FIG. 4A illustrates an exploded view of an example antenna unitassembly.

FIGS. 4B and 4C are illustrations of an example antenna assembly showingfurther detail.

FIGS. 5A-5D are illustrations of an embodiment of [[a]] an antennasubassembly.

FIG. 6 is a block diagram of an example embodiment of an antenna feedand a distributed transceiver.

FIGS. 7A and 7B illustrate the assembly of antenna feed and integrateddistributed transceiver through an exploded view thereof.

FIGS. 8A and 8B illustrate an example embodiment of an integrateddistributed transceiver antenna feed.

FIGS. 9A-9D depict and example embodiment of a mid-band OMT according toan example embodiment.

FIG. 10 is a high level schematic diagram of an example embodiment of aVSAT system with a compact multi-band antenna feed with agilepolarization diversity and integrated distributed transceiver.

FIG. 11 is a detailed schematic diagram illustrating the electrical andRF connections between elements of an example embodiment of an antennaunit.

FIG. 12 is a high level schematic diagram of a low noise block (LNB)down-converter with gain control and path control.

FIG. 13 is a schematic diagram of an example block up-converter (BUC)with gain and path control.

FIG. 14 is a schematic diagram of a receiver microwave (RF) polarizationcircuit.

FIG. 15 is a schematic diagram of a transmitter microwave (RF)polarization circuit.

FIG. 16 is a table of recorded antenna performance over variousfrequency ranges.

FIG. 17 illustrates the antenna gain of an example embodiment atdifferent frequencies.

DETAILED DESCRIPTION OF THE INVENTION

A description of example embodiments of the invention follows.

A very small aperture terminal (VSAT) is a two-way (i.e. uplink anddownlink) satellite ground station or stabilized mobile terminal,typically with a dish antenna that is smaller than 3 meters (m). VSATscommunicate with satellites in geosynchronous orbit to relay data fromterminals to other terminals in a mesh topology, or master earth stationhubs in a star topology. VSATs are often used with maritime or othermobile platforms.

Traditionally, VSATs are most commonly used to transmit narrowband data.However, with the increased demand for data, including broadbandInternet and high definition television, demand for broadband data hasincreased significantly.

Dual reflector antenna designs, in particular antenna configurationshaving a main reflector and a subreflector, are widely used inmulti-frequency antenna applications to reduce the size of the radomeneeded. One such application is a VSAT antenna. The radome size can bereduced due to the fact that the multi-frequency feed assembly can bearranged between the main reflector and its focal point, thus reducingthe size of the radome needed to provide the antenna structure withenvironmental protection.

Traditional multiple frequency band antenna feeds typically include acommon propagation path, for example, a waveguide along the feed axis.Often, such a waveguide is used to propagate the multiple frequencybands of interest. Typically, individual coupling ports (waveguideirises) are placed at specific locations along the center waveguide.Microwave signals of a specific frequency band couple through thesecoupling ports and propagate to a feed network, which is typicallyconstructed using a waveguide feed network. Waveguide feed networks areusually shaped with different bends and twists. Waveguide networks areused to reduce the attenuation along the propagation path from thecoupling ports to transceivers (or transmitters and/or receivers)because waveguide networks are less than other types of transmissionlines of the same length. However, the bends and twists of a waveguidenetwork increase the waveguide feed network complexity and increaseundesired propagating modes, and, thus, increase RF energy loss.

A rule of thumb used by antenna designers is that gain is directlyproportional to the area of an antenna and indirectly proportional tothe square of the wavelength of the frequency to be used. Therefore,traditional C-band dual reflector antennas are designed to be used withparabolic dishes with diameters approximately 2.4 meters (94 inches) orlarger. For reflector antennas at C-band, the gain of the antennareduces quickly for main reflector parabolic dishes having diametersless than 1-2 meters (m). The gain can be significantly reduced furtherby subreflector and antenna feed blockage. For example, typical C-banddual reflector antennas use a feed assembly with a diameter ofapproximately 17 inches. Because of the gain required in most systems,traditional C-band antennas are quite large. When used in maritimeapplications, C-band antennas occupy a significant amount of valuabletop deck real-estate. In addition to the lost opportunity costsresulting from the real-estate that C-band antennas consume, traditionalC-band antennas also consume more fuel than smaller devices.

A compact multiple frequency band, agile, polarization diverse, antennafeed and integrated distributed transceiver for VSAT systems, accordingto example embodiments of the present invention, greatly reduces thesize of a traditional antenna system. Such a miniaturized antenna feedand integrated distributed transceiver can reduce costs by minimizingweight, associated fuel and lost opportunity costs, while improvingoperational performance, and minimizing the complexities of a VSATsystem installation and operation.

The term multiple frequency bands, multi-frequency bands,multi-frequency and multi-band are used interchangeably throughout thepresent application to refer to multiple bands or groups of frequencieswherein each band or group of frequencies supports multiplecommunications channels.

The term transceiver is used throughout the present application to referto a transmitter and receiver pair or pairs that operate to enablecommunications over a common communications link (e.g., both up-link anddown-link frequency bands). A transmitter and receiver pair may becombined to share common circuitry and may share a common housing.Alternatively, the transmitter and receiver of a receiver pair each maybe housed in a respective transmitter and receiver module and share onlylimited common circuitry, such as a common transmission or receptionpath (e.g., an antenna feed), or may share no circuitry at all.

As used throughout the present application, the term reflector is usedto refer to a device or structure that reflects electromagnetic waves.The term reflector is used to generally refer to the main or primaryreflector, while the term sub-reflector is used generally refer to asecondary reflector (typically smaller).

As used throughout the present application, the term circuit board mayrefer to a printed circuit board (PCB), flexible or non-flexible, or ahybrid thereof (e.g., a combination of flexible and non-flexible circuitboards), single or multi-layer circuit boards, single or multipleintegrated circuits (ICs), also known as chips, and can have atwo-dimensional or three-dimensional architecture.

As used throughout the present application, the term integratedgenerally means to have formed, coordinated, or blended into afunctioning or unified whole, to incorporate into a larger unit, andmore specifically, with reference to an antenna feed assembly withintegrated transceivers, means that the transceivers are tightly coupled(mechanically and electromagnetically) to the antenna feed assembly. Forexample, the integrated transceivers are directly mounted to (directphysical connection) the antenna feed assembly.

An example embodiment of a compact multi-frequency agile polarizationdiversity antenna assembly includes a main reflector, subreflector, andantenna feed in a feed through arrangement with the main feed to coupleof electromagnetic energy between the antenna feed assembly and thesubreflector and main reflector, creating a shadow region or blockagearea between the subreflector and main reflector wherein the antennafeed is located. An example embodiment of the antenna feed assemblyincludes a feed horn, a waveguide assembly including orthomodetransducers, integrated transceivers. The two transceivers can include ahigh band transceiver and a low band transceiver. The high bandtransceiver can be rotated mechanically, relative to the antennaassembly including the low band transceiver in order to facilitate skewalignment (i.e., to line up the high band transceiver with thepolarization of a prospective communication link antenna). The low bandtransceiver can be a distributed transceiver including separatetransmitter and receiver modules. The transmitter and receiver modulesfor the low band transceiver can be coupled to the antenna feed assemblyusing OMTs. The OMTs can couple electromagnetic energy over a receivedand transmit low bands, from irises long sweeping waveguide arms coupledto a the respective transmitter and receiver modules in at a planarinterface. In other words, the receiver module can interface with theOMT in at a planar interface so that the ports of the receiver modulemate with the ports of the OMT in a quadrature arrangement in a singleplane. Such a quadrature arrangement in a single plane facilitatescircular polarization because the lengths of the OMT paths are identicaland equal. As will be presented in more detail below. The low bandreceiver module and low band transmitter module of the low bandtransceiver are disk or ring shaped enabling the high and RF signals topropagate through the waveguide of the antenna feed assembly to the highband transceiver. The low band transceiver and respective transmitterand receiver modules are arranged along the antenna feed waveguideassembly such that the lateral dimensions (e.g., the diameters) arecontained within the shadow region or blockage area of the subreflectorbetween subreflector and the main reflector.

An example embodiment of a compact multi-frequency agile polarizationdiverse antenna feed can be integrated with multiple transceivers,including a distributed transceiver waveguide includes receiver andtransmitter modules arranged along the multi-frequency feed path. Thereceiver and transmitter modules can be coupled to the waveguide pathusing respective orthomode transducers (OMTs) having ports arranged inquadrature aligned in a single plane positioned as close as practicableto the signal coupling irises located along the multi-frequency feedpath, so that transmission line losses are minimized. In an exampleembodiment, a set of short waveguide bends with frequency rejectingfilters are used to couple the RF signals of interest from themulti-frequency feed path to the receiver and transmitter modules. Eachset of short waveguide bands provides an equal length propagation pathand four ports in a quadrature arrangement to provide a planar interfaceto the transmitter and receiver modules, respectively.

An example embodiment of the compact, multi-frequency, agile,polarization diverse, antenna feed and integrated distributedtransceiver provides a miniaturized and lightweight feed system. Thesystem performance of an example embodiment is an improvement overtraditional VSAT systems in part due to the minimization of insertionloss and phase mismatch. In an example embodiment, the diameter of theantenna feed is less than 8 inches, where the diameter is the lateralcross-section of the antenna feed. Such a small diameter enables a small42.3 inch reflector main reflector to be used while still maintainingsystem link budgets. Example embodiments presented work efficiently atC-band and Ku-band.

An example embodiment of the antenna system presented herein can operateover the following approximate frequency bands and wavelengths:

C-Rx 3.60-4.20 GHz, free space wavelength 7.10-8.30 cm;

C-Tx 5.85-6.25 GHz, free space wavelength 4.80-5.10 cm;

Ku-Rx 11.7-12.7 GHz, free space wavelength 2.40-2.56 cm; and

Ku-Tx 14.0-14.5 GHz, free space wavelength 2.07-2.10 cm.

An example embodiment of the compact, multi-frequency, agilepolarization diversity antenna assembly VSAT terminal can supportseamlessly both C-band and Ku-band services, which can include CDMAcommunications, Voice over Internet Protocol (VoIP), Ethernet, Wi-Fi,Internet, etc.

FIG. 1A depicts an example application of an example embodiment of thepresent invention. A maritime vessel 101 uses a very small apertureterminal (VSAT) 105 (shown in FIG. 1B) to communicate with a satellite102. The maritime vessel 101 receives a downlink communications 103 aand transmits information via an uplink signal 103 b to satellite 102using VSAT 105. Also depicted in FIG. 1A-1 is a traditional C-bandradome 104. As shown in FIG. 1A-1, an example embodiment of a radome ofan antenna assembly 110 according to an embodiment of the presentinvention is shown relative to the traditional C-band radome 104. Theantenna assembly 110 includes compact, multi-frequency, antenna feed andintegrated distributed transceiver (shown in FIG. 2), whichsignificantly reduces the antenna dimensions required and, therefore,the dimensions of the radome required.

FIG. 1B shows a VSAT 105 including an antenna unit 110 and below deckequipment 107. The antenna unit 110 includes the antenna assembly 111and radome 112. The antenna assembly 111 includes a reflector 120mounted to a mechanical scanning assembly 115. The mechanical scanningassembly 115 further includes motor and control mechanisms (not shown).The mechanical scanning assembly 115 includes three axes of motion,enabling the antenna to provide azimuth, elevation, and cross-azimuthcoverage. The mechanical scanning assembly 115, includesgyro-stabilization, robotic, direct-drive motion control and a modularantenna controller for high-speed tracking. The three-axis,gyro-stabilized, pedestal design, mechanical scanning assembly 115 andfourth-axis skew adjustments, as will be presented in more detail below,enables the optimal satellite in the network to be tracked, includingdirectly overhead at the equator and the horizon at polar latitudes.

FIG. 2 depicts today's satellite coverage map 200 for a dual-frequencyVSAT assembly. In the example embodiment illustrated, Ku-band coveragewith C-band overlay coverage, Ku-band coverage only, and C-band'scoverage only, are shown. As can be seen from the coverage map 200,satellite communications coverage for Ku-band and C-band overlay isavailable over most of the globe, coverage of 95% of the Earth'ssurface, with exception of the poles.

FIG. 3 illustrates a significant reduction in size possible with anexample embodiment of the present invention. For the example embodimentshown in FIG. 3, a C-band miniaturized antenna feed and distributedintegrated transceiver enables the diameter of the radome 312, which isapproximately 124 cm (49 inches), to be reduced by about 66% from thatof the standard C-band radome 304, which has a diameter of about 366 cm(144 inches). Not only is space and real-estate footprint saved using anembodiment of the present invention, weight savings of roughly 85% canalso be achieved (e.g., from a weight of about 680 kg (1500 lbs) for thetraditional antenna to a weight of 102 kg (225 lbs) for the exampleembodiment).

FIG. 4A illustrates an exploded view of an example antenna assembly 410.The antenna assembly 410 includes three subassemblies, a radomesubassembly, antenna subassembly 420, and a mechanical scanning assembly415. The radome subassembly includes a radome 412 and base unit 413. Thebase unit 413 includes a hatch 414, which enables access to the interiorfor service and maintenance. Mechanical scanning assembly 415 includessupport structures, mechanical drive mechanisms (e.g., a roboticdirect-drive assembly), and associated controlling electronics (notshown in detail) to scan and control the speed and direction in whichthe antenna beam is pointing. Antenna subassembly 420 includes reflector421, miniaturized antenna feed and integrated transceiver assembly 430,subreflector 431, and GPS assembly 417. In the example embodiment ofFIG. 4A, reflector 421 is a parabolic dish. Antenna subassembly 420includes a rear-fed reflector 421 and antenna feed and integratedtransceiver assembly 430, which can be seen to be protruding through tothe front side of reflector 421. The front side is on the same side asthe face of the parabolic dish that reflects RF energy and the side thatincludes boresight.

FIGS. 4B and 4C are illustrations of the antenna assembly 410 showingfurther detail. FIG. 4B illustrates a perspective view of the antennaassembly 410 with boresight, that is the direction in which the antennabeam is pointing, being at a roughly 45 degree angle into the page, awayfrom the viewer. FIG. 4C illustrates a perspective of the antennaassembly 410 with the beam pointing out of the page, towards the viewerat an approximately 30 degree angle. FIG. 4C is a front side view of theantenna assembly 410.

FIG. 4B illustrates a back side view of the antenna assembly 410. Theantenna assembly 410 includes an antenna radome subassembly (radome 412and radome base unit 413), mechanical scanning subassembly 415, andantenna subassembly 420. The back side view of the antenna subassembly420 further shows main reflector 421, and antenna feed and integratedtransceiver assembly 430.

From FIG. 4B and FIG. 4C, it should be clear that the antennasubassembly 410 is a rear-fed reflector, with the antenna feed assembly430 protruding from the backside of reflector 42. In a preferred exampleembodiment, the antenna feed assembly 430 is arranged to pass-throughthe vertex of the parabolic dish main reflector 421 to the front side ofthe antenna main dish reflector 421. The lateral cross-sectiondimensions (e.g., diameter) of the antenna feed 430 are smaller than thelateral cross-section dimensions antenna subreflector 431.

To achieve efficient radiation characteristics, a subreflector (orsub-dish), such as a subreflector 431, must be at least a fewwavelengths in diameter. However, the presence of the subreflector 431introduces electromagnetic shadowing onto the main reflector 421. Suchshadowing is a principal performance limitation of microwave antennaswith subreflectors. Shadowing can significantly degrade the gain of anantenna system, whether caused by the subreflector 431 or antenna feed430, or a combination thereof. Example embodiments of miniaturizedantenna feed and distributed integrated transceiver presented canminimize main reflector shadowing, thereby enabling a smaller mainreflector 431 to be used while maintaining antenna gain and efficiency.

FIG. 5A shows a front perspective view of an example embodiment of anantenna subassembly 520. The antenna subassembly 520 includes shapedparabolic dish 521, which acts as a main reflector, and antenna feedassembly including integrated distributed transceiver assembly 530,subreflector 531, and global positioning system (GPS) assembly 517. Theexample embodiment of the miniaturized compact multi-frequency agilepolarization diversity antenna feed and integrated distributedtransceiver assembly 530 is arranged such that it feeds the mainreflector, parabolic shaped dish 521, from the rear, via reflectionsfrom the subreflector 531. As such, the example embodiment of antennaassembly 520 is a rear-fed reflector antenna.

FIG. 5B is an exploded view of the antenna subassembly 520. FIG. 5Bshows main reflector 521 in a rear-fed arrangement, where antenna feedassembly with integrated transceiver distributed transceiver 530 isarranged to have a rear portion located on the back side of the mainreflector 521 while a front portion of feed assembly 530 protrudes tothe front side of the main reflector 521 and feeds subreflector 531. Theantenna feed assembly 530 includes a subreflector 531, feed horn 532,low frequency band transceiver 540, high frequency band transceiver 550.One of skill in the art will appreciate that at a high level the lowband and high band transceivers of the example embodiment can be viewedas a distributed transceiver. One of skill in the art will furtherappreciate that the transmitter and receiver pair of a transceiver canbe housed in separate modules that are arranged in a further distributedfashion and also may be referred to as a distributed transceiver.

FIG. 5C is a depiction of the antenna subassembly 520 that furtherillustrates the antenna feed with the integrated distributed transceiver530 arranged to protrude through the parabolic dish 521 from the rear.The antenna feed assembly 530 couples electromagnetic energy (RF ormicrowave signals) to and from the subreflector 531, which reflects theelectromagnetic energy to main reflector 521.

FIG. 5D is a perspective drawing of a simplified example antennaassembly 520. The antenna assembly 520 includes a parabolic dish mainreflector 521 and antenna feed assembly 530 with integrated distributedtransceiver. The antenna feed assembly 530 includes a subreflector 531,feed horn 532, waveguide assembly 553, high-band transceiver 550, andlow-band distributed transceiver 540.

The subreflector 531 creates a blockage (or shadow) region 533 betweenthe main reflector 521 and subreflector 531 that blocks electromagneticenergy. The low-band distributed transceiver 540 includes low-bandreceiver module 541 and low-band transmitter module 545, each configuredto allow waveguide assembly 553 to pass through and propagate high-bandsignals. The low-band receiver module 541 is further arranged such thatit is substantially orientated within the blockage region 533. Thelow-band receiver module 541 and low-band transmitter module 545 arecoupled to respective low-band receiver and low-band transmitter OMTsvia microwave ports arranged in a quadrature configuration. The OMTs canbe integrated with the waveguide assembly 553 and can act as amultiplexer to couple the RF signals of the frequency band to theassociated with the low-band receiver module 541 or low-band transmittermodule 545. The microwave ports of the respective OMTs terminate in asingle plane, which enables a planar interface to couple to therespective low-band receiver and transmitter, and ensures that the phaselengths of the quadrature RF paths are identical.

The antenna assembly 520 is used to receive downlink signals 503 a_(LP), 503 a _(CP) and transmit uplink signals 503 b _(LP), 503 b _(CP).For example, the receive downlink signals can be a high-band receivesignal 503 a _(LP), such as a Ku-band receive signal, or a low-bandreceive signal 503 a _(CP), such as a C-band receive signal. Thelow-band signal 503 a _(CP) can be a circularly polarized signal (righthand or left hand circular polarization). The high-band receive signal503 a _(LP) can be a linearly polarized signal. To reduce polarizationmismatch loss, the high-band transceiver 550 can be mechanically rotatedto match the linear polarization of the antenna assembly 520 with thedownlink signal 503 a _(LP). Such physical rotation of the high-bandtransceiver 550 enables skew alignment. Further, the transmit uplinksignals can be a high-band transmit signal 503 b _(LP), such as aKu-band transmit signal, or a low-band transmit signal 503 b _(CP), suchas a C-band transmit signal. The low-band signal 503 b _(CP) can be acircularly polarized signal (right hand or left hand circularpolarization). The high-band signal 503 b _(LP) can be a linearlypolarized signal. Similarly to the receive case, the high-bandtransceiver 550 can be mechanically rotated to match the linearpolarization of the antenna assembly 520 for the uplink signal 503 b_(LP) to match the target satellite (skew alignment with the pairedantenna).

FIG. 6 is a block diagram of an example embodiment of an antenna feedand a distributed transceiver 630. The subreflector 631 reflectsmicrowave energy between the waveguide feed horn 632 and the mainreflector (not shown in FIG. 6). The waveguide feed horn (also referredto as simply the feed horn or horn) is an integral part of waveguideassembly 635. Waveguide assembly 635 contains structural features toperform multiple functions. Waveguide assembly 635 can be thought offunctionally as a multiplexor, a passive device that enablesmultiplexing of separate frequency bands on the same channel, and, forexample as a triplexer. The channel with respect to the exampleembodiment of FIG. 6 is the axis of propagation along the center of thewaveguide assembly 635. The three frequency bands can be referred to asa low frequency, middle frequency, and high frequency band or range offrequencies associated with the triplexer. The structural features ofwaveguide assembly 635 include low frequency band orthomode transducer(OMT) 643, middle frequency band OMT 647, and high frequency bandwaveguide 653. The low frequency band OMT 643, middle frequency band OMT647, and high frequency band waveguide 653 are integral parts ofwaveguide assembly 635. It should be understood that the low-band,mid-band and high-band can be utilized such that any one banddesignations can support downlink and uplink channels, while the othertwo bands each individually support a downlink or uplink channel. Forexample, the low-band and mid-band designations can be used to supportC-band downlink and uplink channels, respectively, while the high-banddesignation is used for both downlink and uplink channels at Ku-band.Those with skill in the art will appreciate that the example embodimentspresented are merely illustrative and are not intended as limiting.Under such designations, the waveguide assembly 635 (or antenna feedassembly 630) can be thought of functionally also as a quadplexer,multiplexing four frequency bands (C-band receive, C-band transmit,Ku-band receive, Ku-band transmit).

The OMTs 643, 647 are integral parts of the waveguide assembly 635. Eachof the low and middle frequency band OMTs 643, 647 have four portsarranged in a quadrature configuration. Opposing pairs of the quadratureports are used to create two orthogonal linear polarization senses forthe propagating RF energy. The two orthogonal linear polarization sensescan be for example, vertical and horizontal polarization senses. As willbe presented in more detail below, the two orthogonal linearpolarization senses can be used to create circular polarization senses.

Integrated with the waveguide assembly 635 is a distributed transceiver640. The distributed transceiver 640 includes a receiver module 641 andtransmitter module 645. The receiver module 641 is coupled to a lowfrequency section of waveguide assembly 635 via the OMT 643. The OMT 643selectively couples RF energy having frequencies within the lowfrequency band to the low-frequency band receiver module 641.

The transmitter module 645 of distributed transceiver 640 is coupled tothe OMT 647 section of the waveguide assembly 635. Waveguide OMT 647selectively couples microwave energy having frequencies within the rangeof the middle frequency band from the transmitter module 645.

The waveguide assembly 635, including the integrated low and middlefrequency band OMTs 643, 647, enables RF energy having frequencies inthe high frequency band to propagate to the high frequency bandwaveguide 653. The dimensions of waveguide 653 are those of assembly635, including OMTs waveguide with frequencies sections 643, 647. Thehigh frequency band waveguide 653 acts as a high-pass filter, rejectingmicrowave energy in the lower frequency bands (e.g., frequencies of thelow and middle frequency bands) and allowing microwave energy havingfrequencies above the cut-off frequency (e.g., frequencies within thehigh frequency band) to propagate. A high frequency OMT 657 is used toseparate the high-frequency band microwave energy into two orthogonallinear polarized senses. The OMT 657 is coupled to a high frequency bandtransceiver 650. Transceiver 650 includes high frequency band receivermodule 651 and high-frequency band transmitter module 655. The highfrequency OMT 657 can operate as a diplexer to diplex the high bandreceive and transmit signals.

In the example embodiment shown in FIG. 6, transmit signals aretransferred from a modem (not shown) to a switch and signal levelcontroller module 680. From switch and signal controller module 680 thetransmit signals are provided to the high frequency band transmittermodule 655 via cable 681, or alternatively, depending upon the frequencyof the uplink channel that the VSAT system is communicating with, tomiddle frequency band transmitter module 645 via cable 682. RF signalsreceived at the high frequency receiver module 651 are down-convertedfrom the high frequency to an intermediate frequency (IF), then outputto low frequency band receiver module 641, via cable 683. The signalsreceived at low frequency band receiver module 641 are converted down toa second IF. (The first and second IFs may be in the same frequencyband). The second IF signals are transferred via signal cable 684 to thereceive modem (now shown). A switch and signal control module (notshown) similar to that of switch band signal control module 680 is usedin connection with low band receiver module 641 to switch betweenreceiving RF signals having frequencies within the low and high bands(e.g., switching between receiving C-band and Ku-band) and to adjust thesecond IF signal level.

FIG. 7 depicts an example embodiment of a miniaturized antenna feed andintegrated transceiver assembly 730. The exploded views of FIG. 7illustrates the assembly of antenna feed and integrated distributedtransceiver 730. The antenna assembly 730 is made up of subassemblies,including antenna subreflector 731, waveguide transceiver assembly 735,and high frequency transceiver 750. The waveguide transceiver assembly735 is a waveguide assembly integrated with a distributed transceiversincluding a receive module 741 and transmitter module 745, eachtransceiver operating over a separate frequency band. The waveguidetransceiver assembly 735, as show in FIG. 7B, includes antenna feed horn732, low-band OMT 743, mid-band OMT 747, and high-band waveguide section753. The waveguide transceiver assembly 735 can also optionally includea dielectric rod 759 arranged about the center axis of the waveguidetransceiver assembly 735.

The antenna feed horn 732 acts as a transition between free space andthe waveguide transmission line (waveguide) of waveguide transceiverassembly 735 to better match free-space. The waveguide OMT 743 isintegrally coupled with (i.e., integrated with and coupled to) thecenter waveguide section 734. Center waveguide section 734 is theprimary feed path through which the microwave energy of all threefrequency bands of interest propagate. The low-band OMT 743 isintegrally coupled with (integrated with and coupled to) waveguidesection 734 and functions to selectively couple (filter) the low-bandmicrowave signals to the low frequency receiver module 741. The low-bandreceiver module 741 includes a planar interface to coupleelectromagnetic signals from the low-band OMT 743 to the low-bandreceiver circuits, which can be printed circuit board (PCB) microstripor stripline circuits, within the low-band receiving module 741. Theplanar interface is an interface in which all of the microwave portsshare a common unitary interface plane. The low-band receiver module 741is disk shaped, having a hole at its center, to enable the higherfrequency bands of microwave energy to propagate through it unimpededand continue along the axis of propagation of waveguide section 734.Such an arrangement of disk-shaped receiver module 741 and waveguidesection 734, allows the higher frequency signals to pass through thelow-band receiver module 741 without loss while minimizing low-bandfront-end loss and the system noise floor by reducing transmission lineloss to the low-band receiver module 741. The arrangement andconfiguration of the disk-shaped low-band receiver module 741 improvesthe system gain over temperature (G/T) performance. The reduced low-bandfront-end loss allows a smaller sized antenna to maintain an adequatelink-budget for satellite communications.

The mid-band OMT 747 is integrated with the waveguide section 734 andselectively couples the middle range frequencies from the transmittermodule 745 into the antenna feed waveguide section 734 for propagationand transmission as an uplink signal 103 b to a satellite 102 (as shownin FIG. 1A). Similar to the low-band receiver module 741, the (low-band)transmitter module 745 is disk-shaped (having a hole about a centeraxis) and arranged such that the higher frequency signals can passthrough the transmitter module 745 unimpeded to high frequencytransceiver module 750. The optional dielectric rod 759 is a preferredembodiment and is used to facilitate the transmission of the higherfrequency signals within the waveguide section 734.

FIG. 7A is an assembly drawing of transceiver module 750. Thetransceiver module 750 includes high-band receiver module 751, high-bandtransmitter module 755, and high-band OMT assembly 757. In the exampleembodiment of FIG. 7, the high frequency transceiver module 750 uses twoorthogonal linear polarization senses. One polarization sense is usedfor transmitting the uplink signal 103 b to the satellite 102 (shown inFIG. 1A), and the other diverse linear polarization is used to receivethe downlink signal 103 a from the satellite 102. For example, thetransceiver module 750 may use vertical polarization for downlinks andhorizontal polarization uplinks or vice versa.

Further, in order to facilitate skew alignment, the alignment needed tomatch the polarization of the satellite signals, the high-bandtransceiver module 750, including high-band OMT, assembly 757, can berotated mechanically relative to the orientation of the antennasubreflector 731, antenna feed horn 732, waveguide transceiver assembly735, including the receiver module 741 and transmitter module 745.Because receiver module 741 and transmitter module 745 are mechanicallyand electromagnetically coupled to low-band OMT 743 and mid-band OMT747, respectively, and the low and mid-band OMTs 743, 747 are integratedparts of waveguide assembly 735, the miniaturized antenna feed andintegrated distributed transceiver 730 and main reflector (not shown inFIG. 7) are stationary relative to each other.

The transceiver module 750, as shown in assembly drawing FIG. 7A,includes a skew drive motor 75550 in addition to the high-band receivermodule 751 (for example a Ku-band Low Noise Block (LNB)), high-bandtransmitter module 755 (for example a Ku-band Block Up Converter (BUC)),and high-band OMT 757. The transceiver module 750 further includeshardware to mount the transceiver module 750 in a rotatableconfiguration to the antenna assembly (for example antenna assembly520). The hardware includes connector mounting plates 7552, 7554, drivepulley 7556, bearing assembly 7558, OMT adaptor 7562, drive belt 7564,as well as other linking hardware, such as brackets, screws, etc. Thefirst mounting plate 7552 is used to mount the high-band transceiverassembly 750 to the antenna assembly (e.g., 520). The second mountingplate 7554 mounts the skew drive motor 7550 to the first mounting plate7552. The skew drive motor 7550 directly drives the drive belt 7564. Thedrive belt 7564 rotates the drive pulley 7558 via bearing assembly 7558.OMT adaptor 7562 transitions the waveguide assembly 753 to the OMT 575.As will be understood by those of skill in the art, any suitable meansfor rotating the transceiver module 750 can be used, such as a directdrive motor, step motor, servo, actuator, hydraulic, pneumatic, etc. andare contemplated to be within the scope of this and other embodiments.

FIG. 8A illustrates an example embodiment of an integrated distributedtransceiver antenna feed 835. The integrated distributed transceiverantenna feed 835 includes a feed horn 832, low frequency OMT 843, lowfrequency receiver module 841, mid-frequency OMT 847, mid-frequencytransmitter module 845, and high frequency waveguide section 853. FIG.8A illustrates the distributed yet compact and highly integrated designof the integrated distributed transceiver antenna feed 835.

FIG. 8B is a diagram of the integrated waveguide antenna feed 835without receiver module 841 integrated. FIG. 8B is an isolated view ofthe waveguide antenna feed assembly 835 including integral low andmid-band OMTs 843,847. The antenna feed horn 832 is connected to and canbe manufactured in conjunction with waveguide assembly 834 and low-bandOMT 843. The main path waveguide axis of waveguide assembly 834 isvisible between low-band OMT 843 and mid-band OMT 847. The mid-band OMT847 is coupled to transmitter module planar interface assembly 845. Thehigh-band waveguide section 853 includes a waveguide choke within theinterior chamber to allow only the high frequencies of interest topropagate, thus acting as a matched high pass filter prior to highfrequency OMT 857.

FIGS. 9A-D depict an example embodiment of a mid-frequency OMT 947. Themid-frequency band OMT 947 functions similarly to the low frequency OMTexample embodiments presented herein. The waveguide mid-band OMT 947includes waveguide transmission paths 970 a-d. The waveguide paths 970a-d are configured as sweeping arms arranged in a quadrature formation.Such an orthogonal arrangement enables circular polarization to becreated more easily from opposing pairs of the quadrature ports. Thewaveguide mid-band OMT 947 includes multi-band port 961 and high-bandport 962 arranged at opposing ends of the main propagation path, thecenter axis of the main waveguide section 948. A dielectric rod 959 ispreferably arranged to coincide with the axis of the main propagationpath. The mid-band OMT 947 has quadrature symmetry along its centeraxis, the main propagation path. In the example embodiment of OMT 947shown in FIGS. 9A and 9B, the waveguide arms 970 a-d are the samephysical length and, therefore, phase matched. The equal lengthwaveguide arms 970 a-d a in quadrature physical arrangement (i.e.,orthogonal) and contain irises. The irises are located orthogonal toeach other and coupled to the main waveguide cavity. It should beunderstood by those of skill in the art that phase matched paths can becreated using transmission line types other than waveguide, and phasematched paths of different lengths may be used.

The mid-band waveguide OMT 947 is a six port device. Multi-band port 961can support the propagation of microwave energy having frequencies in amiddle (or low) and high frequency bands, while high-band port 962 cansupport high frequency bands, but not low or mid-bands. The RF choke963, which is formed by waveguide corrugations, acts as a filter andmatching termination to filter out the lower frequency bands frompropagating to high-band port 962 and from reflecting back to multi-bandport 961. The quadrature ports 972 a-d are used to couple transmitsignals from a transmitter (for example, 845) into the mid-band OMT 947for transmission from multi-band port 961. The ports 972 a-d are excitedin opposing pairs, for example, 972 a and 972 c are excited 180° out ofphase with respect to one another. Likewise, ports 972 b and 972 d areexcited 180° out of phase with respect to each other. To create circularpolarization, the pairs of ports are excited 90° out of phase withrespect to each other, (i.e., the port pairs). In other words, port 972a is excited: 90° ahead of port 972 b; 180° ahead of port 972 c; and,270° ahead of 972 d.

FIG. 9B shows a longitudinal cross-sectional view of a mid-band OMT 947.The mid-band OMT 947 includes grooves 963 leading from the irises 974a,c. The waveguide grooves 963 are long and narrow longitudinal channelsthat guide the propagation of orthogonal electric fields components,and, thus, enable increased orthogonal mode propagation in the mainwaveguide section 934. The internal port (or iris) 974 a coupleselectromagnetic energy from the waveguide 934 into the mid-band OMTwaveguide arm 970 a-d. A filter 976 a increases the isolation betweenthe waveguide arm 970 a and the waveguide section 934. Because themid-band OMT 947 is a symmetrical device there are corresponding irises974 b-d and filters 976 b-d for the waveguide arms 970 b-d, respectively(not shown).

FIG. 9C shows a lateral cross-sectional view of the mid-band waveguideOMT 947. The irises 974 a-d can be seen in FIG. 9C to be open to theside wall of main waveguide section 948. The filters 976 a-d can be seento be corrugated waveguide sections.

FIG. 9D shows mid-band OMT 947 coupled to a simplified exampleembodiment of a feed horn 935 and includes dielectric rod 959.

FIG. 10 is a high level schematic diagram of an example embodiment of aVSAT system with a compact multi-band antenna feed with agilepolarization diversity and integrated distributed transceiver, includingthe RF, power, and control connections, as well as the relative positionof the antenna feed assembly and integrated transceiver modules withrespect to the main reflector 1021. With respect to the exampleembodiment of FIG. 10, the low, middle and high frequency bands ofinterest are a C-band downlink channel, C-band uplink channel, andKu-band down/up link channels, respectively. On the front side of themain reflector 1021 is a subreflector 1031, C-banddownlink/low-frequency OMT 1043, C-band downlink low noise block (LNB)1041, C-band uplink (mid-frequency) OMT 1047. A C-band uplink solidstate power amplifier (SSPA) 1045 is at or behind the front side (i.e.,face) of the main reflector 1021.

The schematic diagram, FIG. 10, of antenna system 1005 includes aKu-band (high-band) waveguide section 1053 coupled to a Ku-band OMT1057. The Ku-band OMT 1057 is further coupled to a Ku-band transceivermodule 1050. The Ku-band waveguide section 1053, Ku-band OMT 1057, andKu-band transceiver module 1050 enable the Ku-band downlink and uplinkcommunications. The Ku-band downlink signal received at the Ku-bandtransceiver module 1050 is down-converted to an IF frequency and sentvia cable 1083 to the C-band LNB 1041. At the C-band LNB 1041, thereceived C-band downlink signals are down-converted to another second IFsignal. (The first and second IF signals share a common frequencyrange.) The IF signal received from the Ku-band transceiver module 1050passes through the C-band and LNB 1041. The IF signals are sent to amodem 1090 located below deck via cable 1084, depending on the mode ofoperation.

Uplink signals to be transmitted from the modem 1090 are first sent to aC-band block up converter (BUC) 1046. From the C-band BUC 1046, theuplink signals are then sent to either the Ku transceiver 1050 via cable1081 or sent to C-band SSPA 1045 via cable 1082 after being converted tothe C-band uplink frequency. Such an integrated design utilizes hardwarereuse, further reducing system cost, weight, and size.

FIG. 11 (FIGS. 11A-11L) is a detailed schematic diagram illustrating theelectrical and RF connections between elements of an example embodimentof an antenna unit 110. Ku-band LNB 1151 down converts Ku-band RFsignals to IF signals (IF_(Ku-band)) and couples the IF signals to aC-band LNB 1141. At the C-band LNB 1141, received C-band signals aredown-converted to IF signals (IF_(C-band)) and sent to a power andthermal control module 1196. The down-converted Ku-band signals,IF_(Ku-band), are passed through the C-band LNA 1141, and along with theIF_(C-band) signals, are sent to the power and thermal control module1196. The power and thermal control module 1196 is communicativelyconnected to antenna controller 1195. The power and thermal controlmodule is RF coupled to the below deck modem 1007 (shown in FIG. 10). Anantenna controller 1195 is communicatively coupled to a general packetradio service (GPRS) modem 1190. The uplink transmit signals originateat the below deck modem 1007 and are sent to the C-band BUC 1146. Fromthe C-band BUC 1146, the transmit signals are sent to either the C-bandSSPA 1145 or the Ku-band block up converter (BUC) 1155.

FIG. 12 is a high level schematic diagram of a low-band low noise block(LNB) 1241 down converter with gain control and path control (C-band LNB1241). The C-band LNB 1241 is responsible for receiving and passing IFsignals from the Ku-band down converter. The C-band LNB 1241 alsoreceives C-band downlink signals from the C-band downlink (low-band) OMTvia sweeping arms coupled to the microwave ports 1265 a-d. A microwavecircuit 1242 receives the C-band downlink signals via the low-band OMTports 1265 a-d and amplifies each of the quadrature signals using lownoise amplifiers 1266 a-d. The microwave circuit 1242, and in particularthe LNAs 1266 a-d, set the noise figure for the C-band LNB (low-bandreceiver module) 1241. Further included in microwave circuit 1242, andas will be described in further detail below, are combiners and hybridwith path circular polarization control switch 1267. Circularlypolarized C-band downlink signals are output to a C-band down-convertedmodule 1268. The C-band down-converter module 1268 down converts theC-band downlink signal to an IF signal which is output to themux-circuit module 1271 for multiplexing with Ku-band downlink signals.The multiplexed C-band and Ku-band signals are then output frommux-circuit module 1271 to a gain control circuit 1273 for IF signallevel adjustment. The gain controlled IF signal is then de-multiplexedat demultiplexing circuit 1269, which outputs the demultiplexed IFsignal. A control and power module 1280 interfaces with the mux-circuitmodule 1271 and gain control module 1273 to provide monitoring, control,and power.

FIG. 13 is a schematic diagram of an example C-band BUC 1346 with gainand path control. The C-band BUC 1346 receives uplink signals via thebelow deck modem 1007 (FIG. 10). The uplink signals are de-multiplexedat the de-mux module 1369. The de-mux module 1369 produces an uplinksignal for Ku-band and an uplink signal for C-band and respectivelycouples the uplink signals to a Ku-band gain control module 1373 b and aC-band gain control module 1373 a. The uplink signal for Ku-band is fedto Ku-band mux-circuits module 1371 b. The uplink signal for C-band isfed to C-band up-converter module 1368. A control and power module 1380interfaces with the C-band gain control module 1373 a, C-bandup-converter module 1368, Ku-band gain control module 1373 b, and theKu-band mux-circuits module 1371 b. The C-band up-converter module 1368is electromagnetically coupled to a C-band SSPA module 1045 (FIG. 10).The Ku-band mux-circuits module 1371 b is electromagnetically coupled toa Ku-band transceiver module 1050 (FIG. 10).

FIG. 14 is a schematic diagram of a receiver microwave (RF) polarizationcircuit 1442. The polarization microwave circuit 1442 can be implementedusing any type of transmission line (RF propagation medium), such asmicrostrip, stripline, or a combination thereof. Quadrature ports 1465a-d receive signals from a low frequency OMT 843 (as shown in FIG. 8A).Although other phase matched embodiments can be used, in a preferredembodiment, the microwave coupling interface is planar, that is all fourquadrature ports 1465 a-d interface with low-band OMT 843 in the sameplane. The RF signals received at quadrature ports 1465 a-d areamplified using low noise amplifiers 1466 a-d, respectively. Thequadrature ports 1465 a-d are paired such that the pair of ports areabout 180° out of phase and provide a linear polarization sense. Theamplified RF signals are combined in pairs at combiners 1467 h,v toproduce linear polarization outputs having horizontal and verticalpolarization senses. For example, quadrature port 1465 a is paired withquadrature port 1465 c. When signals from quadrature port 1465 a andquadrature port 1465 c are combined, because they are 180° approximatelyout of phase, the combination produces a horizontal linearly polarizedsignal. Similarly, pairing quadrature ports 1465 b and 1465 d at thecombiner 1467 v produces a vertical linearly polarized signal. A 90°hybrid coupler (also commonly referred to as a ring hybrid or rat-racecoupler) 1467 q is electromagnetically coupled to the linearly polarizedoutputs of the combiners 1467 h,v. The linearly polarized signals areoffset (delayed and advanced) 90° with respect to each other to producea right-hand circular polarization sense output and a left-hand circularpolarization sense output. The functionality of microwave polarizationcircuit 1442, including the combining and phase shifting of thequadrature RF signals can be done electronically (e.g., digitally usinga processor), thus allowing for a dual polarization sense as well aspolarization agility.

The 90° hybrid coupler 1467 q is used to adjust the phase of the RFsignals provided by the combiners 1467 h and 1467 v and properly combinethe RF signals to generate a RHCP or LHCP output. Either a RHCP or LHCPsense signal is received exclusively at any one time. A well matchedtermination is connected to the output port of the ring hybrid coupler1476 q that is not in use. Any undesired signal from the coupler 1476 qis greatly attenuated by the well-matched termination, so that theundesired signal is not reflected back into the coupler 1467 q. The useof such a matched termination on the idling port improves the axialratio of the received circularly polarized signal.

FIG. 15 is a schematic diagram of a transmitter microwave (RF)polarization circuit 1542. In an example embodiment of the presentinvention the transmitter microwave polarization circuit 1542 is used ata middle frequency band. Quadrature ports 1572 a-d are coupled to theports of the middle frequency OMT 947 (FIGS. 9A-D). An uplink transmitsignal, for example, C-band uplink, is input into high-power amplifier1579. A switch 1578 controls the polarization sense by selecting oneport on a hybrid quadrature coupler 1577 q. The hybrid quadraturecoupler 1577 q delays one output 90° in phase with respect to the otheroutput. The outputs of 90° quadrature hybrid coupler are each coupled toa splitter 1577 h,v. The splitters 1577 h,v split their respectiveinputs into two equal output signals 180° out of phase with each other,thus creating a linear polarization sense output. The linearpolarization sense outputs of the splitter 1577 h feeds a pair ofquadrature ports 1572 a,c 180° out of phase from each other. Likewise,the splitter 1577 v feeds the paired quadrature ports 1572 b,d 180° outof phase with respect to each other. Because the 90° quadrature hybridcoupler offsets the signals feeding the splitters 1577 h,v by 90°, andthe paired ports, which can create a linearly polarized sense, have a180° phase offset, a circularly polarized uplink signal is coupled tomid-band OMT 947.

Those of skill in the art will recognize that circular polarization iscreated through circuit 1542 such that the signal transmitted from ports1572 a-d are consecutively 90° out of phase with respect to theneighboring ports. In other words, port 1572 a is 90° out of phase(leading or lagging), from the port 1572 b. 1572 b is 90° leading orlagging from port 1572 c. Port 1572 c is another 90° leading or laggingfrom port 1572 d. Thus, the switch electronically controls whether aright-hand or left-hand polarization sense can be transmitted at themiddle frequency range. The functionality of the microwave transmitterpolarization circuit 1542 including the phase shifting and splitting canbe performed electronically, using software executed by a processor.Alternatively, the agile polarization diversity may be processed bydedicated hardware components, such as Application Specific IntegratedCircuits (ASICs) or Field Programmable Gate Arrays (FPGAs).

A similar technique to improve polarization performance with respect tothe receiver microwave (RF) polarization circuit 1442 (FIG. 14) can beused with respect to the transmitter microwave (RF) polarization circuit1542 as well. The switch 1578 controls the input signal into the 90°hybrid coupler 1577 q. For the input port that is not in use, a wellmatched termination is connected to that port as well. The use of such awell matched termination on the idling port improves the axial ratio ofthe transmitted circularly polarized signal.

FIG. 16 is a table of recorded antenna performance over variousfrequency ranges, such as Ku-band transmit at 14 GHz to 14.5 GHz,Ku-band receive at 10.7 GHz to 12.75 GHz (together the Ku-bands are anexample of a high-band), C-band transmit 5.85 GHz to 6.425 GHz (anexample of a mid-band), and C-band receive at 3.625 GHz and 4.2 GHz (anexample of low-band). An antenna efficiency between 54% and 82% wasrecorded over all frequency bands of interest.

FIG. 17 depicts the antenna gain of an example embodiment at differentfrequencies as a function of degrees off of bore site, bore site beingat 90°. As is shown by the plot of the recorded performance of theantenna feed horn, the performance for the feed cut of 90° is within 2dB for 35° off of boresite for the Ku-band transmit and C-band transmitfrequencies. Thus, the beamwidths and the primary radiation patterns ofthe antenna feed horn at both uplink frequencies of interest aresubstantially similar.

Further example embodiments of the present invention may be configuredusing a computer program product; for example, controls may beprogrammed in software for implementing example embodiments of thepresent invention. Further example embodiments of the present inventionmay include a non-transitory computer readable medium containinginstruction that may be executed by a processor, and, when executed,cause the processor to complete methods described herein. It should beunderstood that elements of the block and flow diagrams described hereinmay be implemented in software, hardware, firmware, or other similarimplementation determined in the future. In addition, the elements ofthe block and flow diagrams described herein may be combined or dividedin any manner in software, hardware, or firmware. If implemented insoftware, the software may be written in any language that can supportthe example embodiments disclosed herein. The software may be stored inany form of computer readable medium, such as random access memory(RAM), read only memory (ROM), compact disk read only memory (CD-ROM),and so forth. In operation, a general purpose or application specificprocessor loads and executes software in a manner well understood in theart. It should be understood further that the block and flow diagramsmay include more or fewer elements, be arranged or oriented differently,or be represented differently. It should be understood thatimplementation may dictate the block, flow, and/or network diagrams andthe number of block and flow diagrams illustrating the execution ofembodiments of the invention.

The teachings of all patents, published applications and referencescited herein are incorporated by reference in their entirety.

While this invention has been particularly shown and described withreferences to example embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

1-21. (canceled)
 22. An antenna feed assembly, comprising: a feed hornconfigured to propagate multiple radio frequency (RF) bands with primaryradiation patterns having substantially the same beamwidth for at leasttwo RF bands of the multiple RF bands; a set of phase matched RF paths,operative over an RF band of the multiple RF bands, electromagneticallycoupled to the feed horn and configured to propagate electromagneticenergy of corresponding polarizations in an orthogonal arrangementaround the feed horn; a receiver module mounted to the feed horn andmechanically and electromagnetically coupled to the set of RF paths; anda subreflector having a lateral cross-section of the same dimension orlarger than a corresponding lateral cross-section of the feed horn andmounted receiver module.
 23. The antenna feed assembly of claim 22,wherein the receiver module further includes an electronic phase shifteroperative to adjust a phase angle of electromagnetic energy received viathe set of phase matched RF paths.
 24. The antenna feed assembly ofclaim 23, wherein the electronic phase shifter of the receiver modulecontrols switching between receiving electromagnetic signals having aright hand circular polarization (RHCP) sense and a left hand circularpolarization (LHCP) sense independently of a transmit function of atransmitter module, the receiver module and transmitter module composinga transceiver.
 25. The antenna feed assembly of claim 22, wherein theset of phase matched RF paths is a first set of phase matched RF pathsand wherein the RF band is a first RF band, and further comprising: asecond set of phase matched RF paths, operative over a second RF band ofthe multiple RF bands, electromagnetically coupled to the feed horn andconfigured in an orthogonal arrangement around the feed horn; and atransmitter module mounted to the feed horn and mechanically andelectromagnetically coupled to the second set of RF paths.
 26. Theantenna feed assembly of claim 25, wherein the transmitter modulefurther includes an electronic phase shifter operative to adjust a phaseangle of electromagnetic energy to be transmitted via the second set ofphase matched RF paths.
 27. The antenna feed assembly of claim 26,wherein the electronic phase shifter of the transmitter module isconfigured to control switching between transmitting electromagneticsignals having a RHCP sense and a LHCP sense independently of a receivefunction of the receiver module.
 28. An antenna assembly, comprising: afeed horn assembly, having symmetry about an axis of propagation; a setof RF propagation paths, electromagnetically coupled to the feed hornassembly and configured to propagate electromagnetic energy of a radiofrequency (RF) band parallel to the axis of propagation; and adistributed receiver coupled mechanically and electromagnetically to theset of RF propagation paths at a set of receive ports.
 29. The antennaassembly of claim 28, wherein the set of RF propagation paths is furtherconfigured in an orthogonal arrangement around the axis of propagationof the feed horn assembly.
 30. The antenna assembly of claim 28, furthercomprising a receiver subcircuit of the distributed receiver, thereceiver subcircuit being arranged to shift electronically a phase ofelectromagnetic energy received at the set of receive ports.
 31. Theantenna assembly of claim 30, wherein the receiver subcircuit of thedistributed receiver enables electronic switching betweenelectromagnetic energy having a right hand circular polarization (RHCP)sense and a left hand circular polarization (LHCP) sense.
 32. Theantenna assembly of claim 28, further comprising: a main reflector; asubreflector, configured to reflect electromagnetic energy propagatingbetween the feed horn assembly and the main reflector, the subreflectorcreating an RF shadow region between the subreflector and the mainreflector, the distributed receiver and set of RF propagation pathsbeing located within the RF shadow region and having respective lateralcross-sections that do not exceed a lateral cross-section of the RFshadow region.
 33. The antenna assembly of claim 28, wherein the set ofRF propagation paths is a first set of RF propagation paths and whereinthe RF band is a first RF band, and further comprising: a second set ofRF propagation paths coupled to the feed horn assembly and configured topropagate electromagnetic energy of a second RF band parallel to theaxis of propagation; and a distributed transmitter circuit coupledmechanically and electromagnetically to the second set of RF propagationpaths at a set of transmit ports.
 34. The antenna assembly of claim 33,wherein the second set of RF propagation paths is further configured inan orthogonal arrangement around the axis of propagation of the feedhorn assembly.
 35. The antenna assembly of claim 33, wherein atransmitter subcircuit of the distributed transmitter is arranged toshift electronically a phase of electromagnetic energy transmitted atthe set of transmit ports.
 36. The antenna assembly of claim 35, whereinthe transmitter subcircuit enables electronic switching betweenelectromagnetic energy having a right hand circular polarization (RHCP)sense and a left hand circular polarization (LHCP) sense.
 37. Theantenna assembly of claim 36, wherein the transmitter subcircuit enablespolarization switching independently of a receive polarization state.38. The antenna assembly of claim 28, further comprising a dielectricrod having an axis coincidental with the axis of propagation of the feedhorn assembly.
 39. An antenna feed assembly, comprising: phase shiftingelectronics, mechanically and electromagnetically coupled to ports ofthe antenna feed assembly; and a controller, operatively coupled to thephase shifting electronics and configured to enable the phase shiftingelectronics to switch between right hand circular polarization (RHCP)and left hand circular polarization (LHCP) senses.
 40. The antenna feedassembly of claim 39, wherein the phase shifting electronics areassociated with a transceiver having a transmitter module and a receivermodule and further configured to switch independently transmitter andreceiver polarization senses. 41-50. (canceled)